3 Answers
3

You should have a look at the log (mysql error log, mysql query log, system logs) entries when the system is misbehaving not after you restart it.

It's likely that you are reaching the max connections limit.

only 50 visitors a day and uses more than 3000 queries per hour

erk, that's absurdly high, even if you are using Hibernate (but you made no mention of what's in between the webserver and MySQL).

I'd be looking to see what's happenning with the web traffic around this time - is it slowing down - are you swapping out too much stuff - exactly how many users are connected. Also check what's happenning with the mysqld process before you try to restart it - is the process still present?